Main features

• :cyclone: Truly Reactive
• :zap: Highly performant and free of memory-leaks
• :twisted_rightwards_arrows: First class support for React Suspense and ready for Concurrent Mode
• :scissors: Decentralized and composable, thus enabling optimal code-splitting
• :microscope: Tiny and tree-shakeable
• :muscle: Supports TypeScript

Table of Contents

• Installation
• API
  • Core
    • connectObservable
    • connectFactoryObservable
    • shareLatest
  • React Suspense Support
    • SUSPENSE
    • suspend
    • suspended
    • switchMapSuspended
  • Utils
    • createInput
• Examples

Installation

npm install re-rxjs

API

connectObservable

const [useCounter, sharedCounter$] = connectObservable(
  clicks$.pipe(
    scan(prev => prev + 1, 0),
    startWith(0),
  )
)

Accepts: An Observable.

Returns [1, 2]

1. A React Hook that yields the latest emitted value of the observable. If the Observable doesn't synchronously emit a value upon the first subscription, then the hook will leverage React Suspense while it's waiting for the first value.

2. A sharedLatest version of the observable that does not complete. It can be used for composing other streams that depend on it. The shared subscription is closed as soon as there are no subscribers to that observable.

connectFactoryObservable

const [useStory, getStory$] = connectFactoryObservable(
  (storyId: number) => getStoryWithUpdates$(storyId)
)

const Story: React.FC<{id: number}> = ({id}) => {
  const story = useStory(id);

  return (
    <article>
      <h1>{story.title}</h1>
      <p>{story.description</p>
    </article>
  )
}

Accepts: A factory function that returns an Observable.

Returns [1, 2]

1. A React Hook function with the same parameters as the factory function. This hook will yield the latest update from the observable returned from the factory function. If the Observable doesn't synchronously emit a value upon the first subscription, then the hook will leverage React Suspense while it's waiting for the first value.

2. A sharedLatest version of the observable returned by the factory function that does not complete. It can be used for composing other streams that depend on it. The shared subscription is closed as soon as there are no subscribers to that observable.

shareLatest

const activePlanetName$ = planet$.pipe(
  filter(planet => planet.isActive),
  map(planet => planet.name),
  shareLatest()
)

A RxJS pipeable operator which shares and replays the latest emitted value. It's the equivalent of:

const shareLatest = <T>(): Observable<T> =>
  source$.pipe(
    multicast(() => new ReplaySubject<T>(1)),
    refCount(),
  )

The enhanced observables returned from connectObservable and connectFactoryObservable have been enhanced with this operator, but do not complete. Meaning that the latest emitted value will be available until the refCount drops to zero.

SUSPENSE

const story$ = selectedStoryId$.pipe(
  switchMap(id => concat(
    SUSPENSE,
    getStory$(id)
  ))
)

This is a special symbol that can be emitted from our observables to let the react hook know that there is a value on its way, and that we want to leverage React Suspense while we are waiting for that value.

suspend

const story$ = selectedStoryId$.pipe(
  switchMap(id => suspend(getStory$(id))
)

A RxJS creation operator that prepends a SUSPENSE on the source observable.

suspended

const story$ = selectedStoryId$.pipe(
  switchMap(id => getStory$(id).pipe(
    suspended()
  ))
)

The pipeable version of suspend

switchMapSuspended

const story$ = selectedStoryId$.pipe(
  switchMapSuspended(getStory$)
)

Like switchMap but applying a startWith(SUSPENSE) to the inner observable.

createInput

A couple examples are worth a thousand words:

const [getCounter$, setCounter] = createInput(0)

const useCounter = connectFactoryObservable((id: string) => getCounter$(id))

const Counter: React.FC<{id: string}> = ({id}) => {
  const counter = useCounter(id);

  return (
    <button onClick={() => setCounter$(id, x => x - 1)} />-</button>
    {counter}
    <button onClick={() => setCounter$(id, x => x + 1)} />+</button
  )
}

or:

const [getUpClicks$, onUpClick] = createInput()
const [getDownClicks$, onDownClick] = createInput()

const useCounter = connectFactoryObservable((id: string) =>
  merge(
    getUpClicks$(id).pipe(mapTo(1)),
    getDownClicks$(id).pipe(mapTo(-1)),
  ).pipe(
    scan((a, b) => a + b, 0),
    startWith(0)
  )
)

const Counter: React.FC<{id: string}> = ({id}) => {
  const counter = useCounter(id);

  return (
    <button onClick={onDownClick} />-</button>
    {counter}
    <button onClick={onUpClick} />+</button
  )
}

Examples

• This is a contrived example based on this example from the React docs.

• A search for Github repos that highlights the most recently updated one:

import React, { Suspense } from "react"
import { Subject } from "rxjs"
import { startWith, map } from "rxjs/operators"
import { connectObservable, switchMapSuspended } from "re-rxjs"
import { Header, Search, LoadingResults, Repo } from "./components"

interface Repo {
  id: number
  name: string
  description: string
  author: string
  stars: number
  lastUpdate: number
}

const searchInput$ = new Subject<string>()
const onSubmit = (value: string) => searchInput$.next(value)

const findRepos = (query: string): Promise<Repo[]> =>
  fetch(`https://api.github.com/search/repositories?q=${query}`)
    .then(response => response.json())
    .then(rawData =>
      (rawData.items ?? []).map((repo: any) => ({
        id: repo.id,
        name: repo.name,
        description: repo.description,
        author: repo.owner.login,
        stars: repo.stargazers_count,
        lastUpdate: Date.parse(repo.update_at),
      })),
    )

const [useRepos, repos$] = connectObservable(
  searchInput$.pipe(
    switchMapSuspended(findRepos),
    startWith(null),
  ),
)

function Repos() {
  const repos = useRepos()

  if (repos === null) {
    return null
  }

  if (repos.length === 0) {
    return <div>No results were found.</div>
  }

  return (
    <ul>
      {repos.map(repo => (
        <li key={repo.id}>
          <Repo {...repo} />
        </li>
      ))}
    </ul>
  )
}

const [useMostRecentlyUpdatedRepo] = connectObservable(
  repos$.pipe(
    map(repos =>
      Array.isArray(repos) && repos.length > 0
        ? repos.reduce((winner, current) =>
            current.lastUpdate > winner.lastUpdate ? current : winner,
          )
        : null,
    ),
  ),
)

function MostRecentlyUpdatedRepo() {
  const mostRecent = useMostRecentlyUpdatedRepo()

  if (mostRecent === null) {
    return null
  }

  const { id, name } = mostRecent
  return (
    <div>
      The most recently updated repo is <a href={`#${id}`}>{name}</a>
    </div>
  )
}

export default function App() {
  return (
    <>
      <Header>Search Github Repos</Header>
      <Search onSubmit={onSubmit} />
      <Suspense fallback={<LoadingResults />}>
        <MostRecentlyUpdatedRepo />
        <Repos />
      </Suspense>
    </>
  )
}

Contributors ✨

Thanks goes to these wonderful people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!